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Abstract:

An image-processor includes an acquiring unit and a correcting unit. The
acquiring unit acquires image data and ambient light data indicating a
degree of a first color temperature with respect to a second color
temperature. The first color temperature represents a color temperature
for a first ambient light. The second color temperature represents a
color temperature for a second ambient light. A first image, which
corresponds to the image data, is perceived in the first ambient light as
an image having one color appearance. The first image is perceived in the
second ambient light as an image having another color appearance. The
correcting unit corrects the image data such that a color appearance of
the first image under the first ambient light are reproduced under the
second ambient light. The correcting unit corrects the image data based
on the ambient light data such that an image based the corrected image
data is brighter as the second color temperature is higher than the first
color temperature and such that the image corresponding to the corrected
image data is darker as the second color temperature is lower than the
first color temperature.

Claims:

1. An image-processor comprising:an acquiring unit that acquires image
data and ambient light data indicating a degree of a first color
temperature with respect to a second color temperature, the first color
temperature representing a color temperature for a first ambient light,
the second color temperature representing a color temperature for a
second ambient light, a first image, which corresponds to the image data,
being perceived in the first ambient light as an image having one color
appearance, the first image being perceived in the second ambient light
as an image having another color appearance; anda correcting unit that
corrects the image data such that a color appearance of the first image
under the first ambient light are reproduced under the second ambient
light, wherein the correcting unit corrects the image data based on the
ambient light data such that an image based the corrected image data is
brighter as the second color temperature is higher than the first color
temperature and such that the image corresponding to the corrected image
data is darker as the second color temperature is lower than the first
color temperature.

2. The image-processor according to claim 1, wherein the ambient light
data indicates the first color temperature and the second color
temperature.

3. The image-processor according to claim 1, wherein the first color
temperature has a first optimum illuminance and the second color
temperature has a second optimum illuminance, andwherein the correcting
unit changes a brightness of the image data based on a ratio between the
first optimum illuminance and the second optimum illuminance for the
second color temperature.

4. An image-processing method comprising:acquiring image data and ambient
light data indicating a degree of a first color temperature with respect
to a second color temperature, the first color temperature representing a
color temperature for a first ambient light, the second color temperature
representing a color temperature for a second ambient light, a first
image, which corresponds to the image data, being perceived in the first
ambient light as an image having one color appearance, the first image
being perceived in the second ambient light as an image having another
color appearance; andcorrecting the image data such that a color
appearance of the first image under the first ambient light are
reproduced under the second ambient light, wherein the correcting
corrects the image data based on the ambient light data such that an
image corresponding to the corrected image data is brighter as the second
color temperature is higher than the first color temperature and such
that the image based the corrected image data is darker as the second
color temperature is lower than the first color temperature.

5. A computer-readable storage medium storing a computer-executable
image-processing program executable on an image-processor, the
image-processing program comprising:instructions for acquiring image data
and ambient light data indicating a degree of a first color temperature
with respect to a second color temperature, the first color temperature
representing a color temperature for a first ambient light, the second
color temperature representing a color temperature for a second ambient
light, a first image, which corresponds to the image data, being
perceived in the first ambient light as an image having one color
appearance, the first image being perceived in the second ambient light
as an image having another color appearance; andinstructions for
correcting the image data such that a color appearance of the first image
under the first ambient light are reproduced under the second ambient
light, wherein the instructions for correcting corrects the image data
based on the ambient light data such that an image corresponding to the
corrected image data is brighter as the second color temperature is
higher than the first color temperature and such that the image based the
corrected image data is darker as the second color temperature is lower
than the first color temperature.

6. An image-processor comprising:an acquiring unit that acquires first
image data and ambient light data indicating a degree of a first color
temperature with respect to a second color temperature, the first color
temperature representing a color temperature for a first ambient light,
the second color temperature representing a color temperature for a
second ambient light, a first image, which corresponds to the first image
data, being perceived in the first ambient light as an image having a
first color appearance;a first converting unit that converts first image
data based on the first color temperature to second image data;a
correcting unit that corrects the second image data such that an image
corresponding to the corrected second image data is brighter as the
second color temperature is higher than the first color temperature and
such that the image corresponding to the corrected second image data is
darker as the second color temperature is lower than the first color
temperature; anda second converting unit that converts the corrected
second image data based on the second color temperature to the third
image data, a second image, which corresponds to the third image data,
being perceived in the second ambient light as an image having a second
color appearance, the first color appearance being the same as the second
color appearance.

[0002]The present invention relates to an image processor, a
computer-readable storage medium storing a computer-executable
image-processing program, and an image processing method for correcting
image data used to render a printed image so that the colors in the
printed image under a reference ambient light are reproduced under
ambient light present where the printed image will be viewed.

BACKGROUND

[0003]Various studies have been conducted on how different ambient lights
(artificial and natural lights) affect humans differently. This effect,
often called the Kruithof effect, indicates the psychological effect that
ambient light has on humans. As shown in the graph of FIG. 6, light with
a low color temperature is not pleasing to humans at high intensities,
but is pleasing at low intensities. On the other hand, light with a high
color temperature is not pleasing to humans at low intensities, but is
pleasing at high intensities. Thus, the range of light intensities
considered to provide pleasing illumination differs according to the
color temperature of the ambient light. In FIG. 6, "A" indicates an
incandescent lighting, "B" indicates a fluorescent lighting (warm white),
"C" indicates a fluorescent lighting (white), "D" indicates a fluorescent
lighting (cool white), and "E" indicates a fluorescent lighting
(daylight).

[0004]Some conventional lighting fixtures have accounted for this Kruithof
effect. For example, one such lighting fixture can emit light in a
plurality of white colors, such as daylight, cool white, white, warm
white, and extra warm white through a combination of blue LEDs having a
high color temperature and yellow LEDs having a low color temperature.
The lighting fixture produces the different white colors by adjusting the
light intensity produced by the blue LEDs while keeping the intensity of
the yellow LEDs fixed. Hence, the light intensity of the lighting fixture
increases when the intensity of the blue LEDs increases (i.e., when the
color temperature rises).

SUMMARY

[0005]However, it is well known that the same object observed under
different ambient light may be perceived to have a different color.
Studies have been conducted in the field of printing to determine whether
it is possible to eliminate such differences in the way colors of a
printed image are perceived when observing the image under different
lighting conditions by correcting the image data.

[0006]However, while studies have been conducted on reproducing colors
under different ambient lighting so that colors appear the same under
each type of lighting, no study has yet been conducted on how to correct
image data representing an image to be printed so that the printed image
is properly perceived in the observation environment.

[0007]In view of the foregoing, it is an object of the present invention
to provide an image processor, a computer-readable storage medium storing
a computer-executable image-processing program, and an image-processing
method capable of correcting image data for an image being printed so
that the printed image is properly perceived in the observation
environment.

[0008]In order to attain the above and other objects, there is provided an
image-processor including an acquiring unit and a correcting unit. The
acquiring unit acquires image data and ambient light data indicating a
degree of a first color temperature with respect to a second color
temperature. The first color temperature represents a color temperature
for a first ambient light. The second color temperature represents a
color temperature for a second ambient light. A first image, which
corresponds to the image data, is perceived in the first ambient light as
an image having one color appearance. The first image is perceived in the
second ambient light as an image having another color appearance. The
correcting unit corrects the image data such that a color appearance of
the first image under the first ambient light are reproduced under the
second ambient light. The correcting unit corrects the image data based
on the ambient light data such that an image based the corrected image
data is brighter as the second color temperature is higher than the first
color temperature and such that the image corresponding to the corrected
image data is darker as the second color temperature is lower than the
first color temperature.

[0009]According to another aspect of the present invention, there is
provided an image-processing method including:

[0010]acquiring image data and ambient light data indicating a degree of a
first color temperature with respect to a second color temperature, the
first color temperature representing a color temperature for a first
ambient light, the second color temperature representing a color
temperature for a second ambient light, a first image, which corresponds
to the image data, being perceived in the first ambient light as an image
having one color appearance, the first image being perceived in the
second ambient light as an image having another color appearance; and

[0011]correcting the image data such that a color appearance of the first
image under the first ambient light are reproduced under the second
ambient light, wherein the correcting corrects the image data based on
the ambient light data such that an image corresponding to the corrected
image data is brighter as the second color temperature is higher than the
first color temperature and such that the image based the corrected image
data is darker as the second color temperature is lower than the first
color temperature.

[0012]According to another aspect of the present invention, there is
provided a computer-readable storage medium storing a computer-executable
image-processing program executable on an image-processor, the
image-processing program including:

[0013]instructions for acquiring image data and ambient light data
indicating a degree of a first color temperature with respect to a second
color temperature, the first color temperature representing a color
temperature for a first ambient light, the second color temperature
representing a color temperature for a second ambient light, a first
image, which corresponds to the image data, being perceived in the first
ambient light as an image having one color appearance, the first image
being perceived in the second ambient light as an image having another
color appearance; and

[0014]instructions for correcting the image data such that a color
appearance of the first image under the first ambient light are
reproduced under the second ambient light, wherein the instructions for
correcting corrects the image data based on the ambient light data such
that an image corresponding to the corrected image data is brighter as
the second color temperature is higher than the first color temperature
and such that the image based the corrected image data is darker as the
second color temperature is lower than the first color temperature.

[0015]According to another aspect of the present invention, there is
provided an image-processor including an acquiring unit, a first
converting unit, a correcting unit, and a second converting unit. The
acquiring unit acquires first image data and ambient light data
indicating a degree of a first color temperature with respect to a second
color temperature. The first color temperature represents a color
temperature for a first ambient light. The second color temperature
represents a color temperature for a second ambient light. A first image,
which corresponds to the first image data, being perceived in the first
ambient light as an image having a first color appearance. The first
converting unit converts first image data based on the first color
temperature to second image data. The correcting unit corrects the second
image data such that an image corresponding to the corrected second image
data is brighter as the second color temperature is higher than the first
color temperature and such that the image corresponding to the corrected
second image data is darker as the second color temperature is lower than
the first color temperature. The second converting unit converts the
corrected second image data based on the second color temperature to the
third image data. A second image, which corresponds to the third image
data, is perceived in the second ambient light as an image having a
second color appearance. The first color appearance is the same as the
second color appearance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]In the drawings:

[0017]FIG. 1 is a block diagram showing a general structure of a
communication system according to an embodiment of the present invention;

[0018]FIG. 2 is an explanatory diagram showing a dialog box of a printer
driver according to an embodiment of the present invention;

[0019]FIG. 3 is a flowchart illustrating steps in an image-printing
process according to an embodiment of the present invention;

[0020]FIG. 4 is a flowchart illustrating steps in a brightness correction
process according to an embodiment of the present invention;

[0021]FIG. 5 is an explanatory diagram showing relative positions of the
target ambient and the observation ambient light in CIE 1931 xy
chromaticity diagram; and

[0023]Next, a preferred embodiment of the present invention will be
described while referring to the accompanying drawings.

1. Overall Structure of Communication System

[0024]FIG. 1 is a block diagram showing the general structure of a
communication system including a personal computer (PC) 1, and a
multifunction peripheral (MFP) 2 that are capable of performing data
communications with each other.

[0025]The PC 1 is a common data processor that includes a controller 11, a
storage unit 12, a communication unit 13, an operating unit 14, and a
display unit 15.

[0026]The controller 11 performs overall control of each component in the
PC 1. The controller 11 includes a CPU 111, a ROM 112, and a RAM 113.

[0027]The storage unit 12 is a rewritable, nonvolatile storage device. In
the preferred embodiment, the storage unit 12 is configured of a hard
disk drive. The storage unit 12 has various programs installed thereon,
including an operating system (OS) 121, an application program 122 for
executing an application such as an image-browsing program, and a printer
driver 123, which is a program that allows the PC 1 to use the MFP 2.

[0028]The communication unit 13 is an interface for performing data
communications with the MFP 2.

[0029]The operating unit 14 is an input device that allows the user to
input instructions through external operations. In the preferred
embodiment, the operating unit 14 is configured of a keyboard and a
pointing device (a mouse, touchpad, or the like).

[0030]The display unit 15 is an output device for displaying various data
in a visual form that the user can understand. In the preferred
embodiment, the display unit 15 is configured of a liquid crystal
display.

[0031]The MFP 2 is a printing device that, in addition to a printer
function, includes a scanner function, color copier function, and the
like. The MFP 2 includes a controller 21, a storage unit 22, a
communication unit 23, an operating unit 24, a display unit 25, a
scanning unit 26, and a printing unit 27.

[0032]The controller 21 performs overall control of each component in the
MFP 2. The controller 21 includes a CPU 211, a ROM 212, and a RAM 213.

[0033]The storage unit 22 is a rewritable, nonvolatile storage device. In
the preferred embodiment, the storage unit 22 is configured of flash
memory. The storage unit 22 stores programs for instructing the CPU 211
to implement processes described later with reference to FIGS. 3 and 4.

[0034]The communication unit 23 is an interface for performing data
communications with the PC 1.

[0035]The operating unit 24 is an input device that allows the user to
input instructions through external operations. The operating unit 24
includes various operating buttons.

[0036]The display unit 25 is an output device for displaying various data
in a visual form that the user can understand. A compact liquid crystal
display is used as the display unit 25 in the preferred embodiment.

[0037]The scanning unit 26 functions to scan images from an original
document set in a prescribed scanning position and to generate image data
representing the scanned image (more specifically, image data expressed
in the RGB color space).

[0039]Next, a brief description will be given of the processes executed on
the communication system according to the preferred embodiment.

[0040]In the PC 1 according to the preferred embodiment, the printer
driver 123 is started when a printing operation is performed in a running
application. When the printer driver 123 is started, a dialog box is
displayed on the display unit 15 for setting printing conditions. After
the user sets printing conditions in this dialog box, the PC 1 (printer
driver 123) issues a print command to the MFP 2 and transmits image data
representing the target image (and specifically image data expressed in
the RGB color space) to the MFP 2. The MFP 2 performs a color conversion
process for converting RGB image data received from the PC 1 together
with the print command to image data in the CMYK color space, whose
colors correspond to the colors of ink in the MFP 2. The MFP 2
subsequently prints an image based on the converted image data (i.e., the
CMYK data).

[0041]The MFP 2 of the preferred embodiment also prompts the user to set
the ambient light used as reference (hereinafter "target ambient light")
and the ambient light in which the printed material is to be viewed
(hereinafter "observation ambient light"). Subsequently, the MFP 2 prints
the image after performing an ambient light correction process for
correcting the image data in order that the colors of the printed image
under the target ambient light are reproduced under the observation
ambient light. That is, a color appearance of the printed image under the
observation ambient light are perceived as a color appearance that is the
same as a color appearance of the printed image under the target ambient
light, by the user.

[0042]Specifically, in the dialog box of the printer driver 123 shown in
FIG. 2, the user can set various data indicating the target ambient light
and the observation ambient light. In the example shown in FIG. 2, the
dialog box includes radio buttons 31 and 41 for the target ambient light
and the observation ambient light, respectively, that allow the user to
select either "Color temperature" or "XYZ values" as the method of
specifying ambient light settings. When specifying the color temperature
setting method, the user can then select a specific color temperature for
the target ambient light and observation ambient light from pull-down
boxes 32 and 42. When specifying the XYZ value setting method, the user
then inputs specific numbers as X, Y, and Z values in respective
numerical input boxes 33 and 43.

[0043]The printer driver 123 of the PC 1 then transmits the data set above
for the target ambient light and observation ambient light together with
a print command to the MFP 2 as target ambient light data (Xt, Yt, Zt)
and observation ambient light data (Xo, Yo, Zo). XYZ values are also
prestored for the color temperatures that can be selected from the
pull-down boxes 32 and 42. Therefore, if the user has selected the color
temperature method, the printer driver 123 transmits these prestored XYZ
values to the MFP 2. Hence, XYZ values representing the color of the
target ambient light and the color of the observation ambient light are
transferred to the MFP 2, regardless of which setting method was
selected. The XYZ values are values within the range 0-100. Before being
used by the MFP 2, they are normalized to values within the range 0-1.

[0044]By prompting the user to specify the target ambient light and
observation ambient light in this way and subsequently performing ambient
light correction on the image data, the MFP 2 can mitigate differences in
how colors of the printed image are perceived due to differences in
ambient light under which the printed image is viewed.

[0045]It is a particular feature of the MFP 2 according to the preferred
embodiment to adjust the brightness of the printed image based on the
color temperature in the observation ambient light in order that the MFP
2 can produce a printed image that can be suitably viewed in the
observation environment. As described above with reference to the
Kruithof effect, light having a low color temperature is not pleasing at
a high intensity, but is pleasing at a low intensity, while light having
a high color temperature is not pleasing at a low intensity, but is
pleasing at a high intensity. Accordingly, the MFP 2 according to the
preferred embodiment corrects image data so that the printed image is
brighter as the color temperature of the observation ambient light is
higher than the color temperature of the target ambient light and so that
the printed image is darker as the color temperature of the observation
ambient light is lower than the color temperature of the target ambient
light.

3. Process Executed by MFP

[0046]Next, detailed steps in the process executed on the MFP 2 will be
described.

[0047]FIG. 3 is a flowchart illustrating steps in an image-printing
process executed by the controller 21 of the MFP 2 (and specifically the
CPU 211) when the MFP 2 receives a print command from the PC 1.

[0048]In S101 at the beginning of the image-printing process, the
controller 21 acquires the target ambient light data (Xt, Yt, Zt) and the
observation ambient light data (Xo, Yo, Zo). This is the data that the
user has previously set using the PC 1.

[0049]In S102 the controller 21 specifies a pixel in the image represented
by the RGB image data received from the PC 1 that has not yet undergone
the process in S103-S110 described next, sets this pixel as the target
pixel for this process (hereinafter referred to as the "process pixel")
and reads the image data (Ri, Gi, Bi) for this process pixel.

[0050]In S103 the controller 21 converts the pixel data for the process
pixel from RGB values to values in a device-independent color space (XYZ
values (Xi, Yi, Zi) in the preferred embodiment) using an input device
profile. In this case, the input device profile is a profile of the
display unit 15 in the PC 1.

[0051]In S104 the controller 21 converts the pixel data (XYZ values) for
the process pixel to CIECAM02 values (Ji, Cai, Cbi) using the target
ambient light data acquired in S101, where the CIECAM02 values are values
in a color appearance model.

[0052]In S105 the controller 21 executes a brightness correction process
to correct the brightness of the image data based on positional
relationship in the color space between the target ambient light data and
the observation ambient light data. While the details of this brightness
correction process will be described later with reference to FIG. 4, the
process serves to correct the brightness of pixel data for the process
pixel so that the brightness is increased as the color temperature of the
observation ambient light is higher than the color temperature of the
target ambient light and decreased as the color temperature of the
observation ambient light is lower than the color temperature of the
target ambient light.

[0053]In S106 the controller 21 determines whether the pixel data, that
includes the corrected brightness in S105, for the process pixel falls
outside the color gamut of the output device. In this case, the output
device is the printing unit 27 of the MFP 2.

[0054]If the controller 21 determines in S106 that the pixel data falls
outside the color gamut of the output device (S106: YES), then the
controller 21 performs gamut mapping in S107 before advancing to S108.
This gamut mapping may be implemented according to a method well known in
the art.

[0055]However, if the controller 21 determines in S106 that the pixel data
lies inside the color gamut of the output device (S106: NO), the
controller 21 skips S107 and advances directly to S108.

[0056]In S108 the controller 21 converts the pixel data for the process
pixel (CIECAM02 values) to XYZ values (Xj, Yj, Zj) using the ambient
light data for the viewing environment. Since the color conversion
process performed in S104 to convert XYZ values to CIECAM02 values was
implementing using the target ambient light data, the controller 21 can
perform ambient light correction on image data representing the image
being printed so that the colors in the printed image under the target
ambient light are reproduced under the observation ambient light.

[0057]In S109 the controller 21 converts the pixel data for the process
pixel from the XYZ values to RGB values (Rj, Gj, Bj), which are values in
a device-dependent color space, using the output device profile.

[0059]In S111 the controller 21 determines whether the process in
S103-S110 has been completed for all pixels in the image data.

[0060]If the process has not been performed on all pixels of the image
data, the controller 21 returns to S102 (S111: NO), specifies a different
pixel that has not yet been processed as the process pixel, and repeats
the process in S103-S110.

[0061]However, if the controller 21 determines in S111 that the process
has been completed for all pixels (S111: YES), in S112 the controller 21
performs a process to print an image based on the pixel data sets
acquired by the process in S102-S110, and subsequently ends the current
image-printing process.

[0062]Next, the brightness correction process executed by the controller
21 in S105 of the image-printing process described above will be
described with reference to the flowchart in FIG. 4.

[0063]In S201 at the beginning of the brightness correction process, the
controller 21 calculates relative positions of the target ambient light
(Xt, Yt, Zt) and the observation ambient light (Xo, Yo, Zo) in the CIE
1931 xy chromaticity diagram. Specifically, as illustrated in FIG. 5, the
controller 21 sets points Pt' and Po' by mapping a point Pt for the
target ambient light and a point Po for the observation ambient light on
a line segment connecting a point P30 for light having a color
temperature of 3000K to a point P50 for light having a color temperature
of 5000K in the xy chromaticity diagram. In this example, the points Pt'
and Po' are mapped to intersections between the line segment and normals
to the line segment passing through the respective points Pt and Po. The
points P30 and P50 are connected by a straight line (line segment)
because it is presumed that a portion of the black-body radiation curve
approaches a straight line.

[0064]An optimum illuminance V(Pt) for the target ambient light and an
optimum illuminance V(Po) for the observation ambient light are found by
assigning 300 lux to the optimum illuminance V(P30) in lighting having a
color temperature of 3000K and assigning 750 lux to the optimum
illuminance V(P50) in lighting having a color temperature of 5000K based
on the Kruithof effect shown in FIG. 6. However, settings for optimum
illuminance are not limited to the values in this example.

[0065]More specifically, optimum illuminances V(Pt) and V(Po) can be found
for the target ambient light and observation ambient light from Equations
(1) and (2) below, where a distance d between the points P30 and P50 is
normalized to 1, dt represents the distance between the points P30 and
Pt', and do represents the distance between the points P30 and Po'.

Equation 1

V(Pt)=300×(1-dt)+750×dt (1)

Equation 2

V(Po)=300×(1-do)+750×do tm (2)

[0066]Hence, Equations (1) and (2) simplify the Kruithof effect for the
color temperature of commonly used ambient lighting. By finding
interpolation values for points Pt' and Po', it is possible to find the
illuminances V(Pt) and V(Po) that approach optimum illuminances for
points Pt and Po. Here, it is reasonable to find the illuminances V(Pt)
and V(Po) that approach optimum illuminances since the boundary between
pleasing and unpleasing light according to the Kruithof effect is
somewhat vague.

[0067]Next, in S202 the controller 21 finds a gamma value to be used in
the gamma correction process of S203 from Equation (3) below based on the
illuminances V(Pt) and V(Po) calculated in S201. Equation (3) is found
from Equation (4), which signifies that the integral after gamma
correction divided by the integral before gamma correction equals the
optimum illuminance at Po divided by the optimum illuminance at Pt. In
other words, the controller 21 calculates a gamma value for changing the
brightness of the printed image based on the ratio between the optimum
illuminance for the color temperature of the target ambient light and the
optimum illuminance for the color temperature of the observation ambient
light.

[0069]By performing gamma correction in this way, the controller 21 can
correct brightness in the image data to a greater brightness as the color
temperature of the observation ambient light is higher than the color
temperature of the target ambient light and to a lesser brightness as the
color temperature of the observation ambient light is lower than the
color temperature of the target ambient light. By correcting only
brightness in the image data, the appearance of the color hues is
preserved.

4. Effects of the Embodiment

[0070]As described above, the MFP 2 according to the preferred embodiment
performs ambient light correction to correct image data representing an
image to be printed so that the colors in the printed image under the
target ambient light are reproduced under the observation ambient light.
In addition, the MFP 2 corrects the image data using a gamma value for
adjusting the brightness of the printed image so that the printed image
becomes brighter as the color temperature of the observation ambient
light is higher than the color temperature of the target ambient light
and becomes darker as the color temperature of the observation ambient
light is lower than the color temperature of the target ambient light.
More specifically, the MFP 2 changes the brightness of the printed image
based on a ratio between the optimum illuminance for the color
temperature of the target ambient light and the optimum illuminance for
the color temperature of the observation ambient light, making the
printed image brighter as the color temperature of the observation
ambient light is higher than the color temperature of the target ambient
light and darker as the color temperature of the observation ambient
light is lower than the color temperature of the target ambient light.

[0071]Accordingly, the MFP 2 according to the preferred embodiment can
correct the printed image to a suitable brightness based on the Kruithof
effect, without simply correcting the difference in how colors of the
printed image appear due to a difference in the ambient light at which
the printed image is observed.

6. Another Embodiment

[0072]While the invention has been described in detail with reference to
the specific embodiment thereof, it would be apparent to those skilled in
the art that various changes and modifications may be made therein
without departing from the spirit of the invention.

[0073]6-1. Color Space

[0074]In the preferred embodiment described above, gamut mapping is
performed after converting the RGB values to CIECAM02 values. However,
the color space in which gamut mapping is performed may be any uniform
color space and is not limited to the CIECAM02 color space. A uniform
color space is constructed so that the color difference perceived by
humans is comparable to the Euclidean distance in the color space. Other
examples of uniform color spaces are CIELAB and CIELUV.

[0075]6-2. Image-Printing Process

[0076]In the preferred embodiment described above, the MFP 2 performs an
image-printing process based on the sequence of steps in S101-S112.
However, this process may be simplified by first creating an LUT that
defines correlations between the pixel data prior to executing the
process in S103-S110 and the pixel data after executing these processes.

[0077]6-3. Image Data

[0078]In the preferred embodiment described above, the image data inputted
in the MFP 2 is expressed in the RGB color space. However, the present
invention may be applied to inputted image data expressed in another
color space.

[0079]Further, it is not essential that the image data is transferred from
the PC 1, as described in the preferred embodiment. For example, the
image data may be generated by the scanning unit 26 of the MFP 2 or may
be read from a memory card or other portable storage media when the MFP 2
is capable of directly reading image data from such media. Further, the
MFP 2 may be configured to prompt the user to set ambient light data for
the target and ambient light data for the observation environment so that
the ambient light correction process can be executed on the MFP 2 without
the MFP 2 being connected to the PC 1.

[0080]6-4. Ambient Light Data

[0081]In the preferred embodiment described above, the user is prompted to
set ambient light data for a target and an observation environment as
color temperatures or XYZ values. However, the user may also be allowed
to select a type of lighting, for example, such as fluorescent lighting,
incandescent lighting, and the like. Such a selection method may be more
user-friendly than setting the color temperature.

[0082]It is also not essential that the user be required to set the
ambient light data for the target and the observation environment. For
example, the MFP 2 may be provided with a sensor for measuring ambient
light and may automatically set the ambient light data based on the
measured values. In this case, the MFP 2 may measure the ambient light
data of the target using the sensor, while the user is prompted to input
ambient light data for the observation environment.

[0083]It is also not essential that ambient light data (color temperature)
be set for both the target and the observation environment. For example,
the user may set a relative value comparing the ambient light data for
the observation environment to the ambient light data for the target.

[0084]6-5. Printing Unit

[0085]In the preferred embodiment described above, the printing unit 27 is
an inkjet device that prints images using the four ink colors C, M, Y,
and K. However, the printing unit may be configured to use more colors of
ink, for example. Further, the colorant is not limited to ink. For
example, the printing unit may have a laser transfer system for forming
images using toner in a plurality of colors.

[0086]6-6. Image Processor

[0087]In the preferred embodiment described above, the MFP 2 serves as an
example of the image processor according to the present invention.
However, the image processor may be a printing device that does not have
a scanner function or the like. Further, the image processor is not
limited to a printing device. For example, the PC 1 may also function as
the image processor of the present invention. In this case, the printer
driver 123 in the PC 1 executes the process described in S101-S111, for
example, and the PC 1 subsequently transfers the processed image data to
the MFP 2 for printing.